1. Field of the Invention
The present invention relates to an organic electro-luminescence display element including a pair of electrodes and a film (organic electro-luminescence film), located between the electrodes, made of an organic compound and having an organic luminescent layer.
Further, the invention relates to a finder screen display device for displaying information in a finder screen (view-finder screen) of an optical device such as a shooting device (e.g., a camera), a telescope or a microscope which is provided with a finder. For example, the invention relates to the finder screen display device which can display information (e.g., shooting conditions such as a shift of a shooting scope on the finder screen, shooting mode and brightness of a shooting target) superimposed on the image viewed through the finder when using the shooting device such as a camera.
The invention also relates to a finder provided with the foregoing finder screen display device, and an optical device provided with this finder.
2. Description of the Background Art
In recent years, various kinds of information devices have been developed, and thereby there has been the growing need for flat display elements having thin forms and requiring lower power consumption than CRTs. Such flat display elements may be a liquid crystal display element, a plasma display (PDP).and others. In particular, attention has been directed to an electro-luminescence element which is of a self-luminescent type and can make clear display with a large angle of view.
The electro-luminescence elements can be roughly divided into an inorganic electro-luminescence element and an organic electro-luminescence element based on materials forming the elements. The inorganic electro-luminescence elements are already put into commercial products.
However, light emission of the inorganic electro-luminescence element is of a so-called collision excitation type, in which electrons accelerated by an applied high electric field collide with luminescent center for emitting light. Therefore, a high voltage of 100 V or more must be applied for driving the element. This increases a cost of peripheral devices. Since a good luminophor for blue is not available, display in full color cannot be performed by the inorganic electro-luminescence element.
In contrast to the above, the organic electro-luminescence element (organic EL element) is of a so-called injection type, in which the charges (holes and electrons) injected from positive and negative electrodes are recoupled to form excitons in the luminophor, and the excitons excite molecules of luminescent material to emit the light. Therefore, the organic EL element can be driven with a low voltage. Further, it is easy to change the molecular structure of the luminescent material because it is the organic material. Thereby, the color of emitted light can be arbitrarily determined. Accordingly, the organic electro-luminescence element is a significantly promising display element.
The prototype of the organic electro-luminescence element has a two-layer structure provided with a hole transport layer and an electron transport layer. This element was proposed by Tang and Vanslyke [C. W. Tang and S. A VanSlyke; Appl. Phys. Lett., 51 (1987) 913]. This element is formed of a positive electrode, a hole transport layer, an electron transport luminescent layer and a negative electrode which are layered on a glass substrate.
In this element, the hole transport layer functions to inject holes from the positive electrode into the electron transport luminescent layer. The hole transport layer also prevents electrons, which are injected from the negative electrode, from escaping into the positive electrode without being recoupled with the holes, and thereby functions to confine electrons in the electron transport luminescent layer. Owing to the electron confining effect by the hole transport layer, therefore, recoupling between the electrons and holes occurs more efficiently than the element of a single luminescent layer structure, and therefore allows significant reduction in drive voltage.
Further, Saito et al. have disclosed the fact that, in the element of the two-layer structure, not only the electron transport layer but also the hole transport layer can become a luminescent layer [C. Adachi, T. Tsutsui and S. Saito; Appl. Phys. Lett., 55 (1989) 1489].
Saito et al. have proposed, as an improvement of the element of the two-layer structure, an element of a three-layer structure in which a luminescent layer is interposed between the hole and electron transport layers [C. Adachi, T. Tsutsui and S. Saito; Jpn. J. Appl. Phys. 27 (1988) L269]. This element is formed of a positive electrode, a hole transport layer, a luminescent layer, an electron transport layer and a negative electrode layered on a glass substrate. The hole transport layer functions to confine the electrons in the luminescent layer, and the electron transport layer functions to confine the holes in the luminescent layer so that the luminescence efficiency is further improved.
The negative electrode of the organic electro-luminescence element is generally formed of a film of about 100 nm in thickness, which is made of metal having a small work function and is prepared by vapor deposition on an organic layer, and is opaque. In the organic electro-luminescence element, if transparent electrodes are used not only in the positive electrode but also in the negative electrode, the element forms a self-luminescent element having transparency so that it can be applied to a wider range.
In connection with this, a transparent organic electro-luminescence element is disclosed in Japanese Laid-Open Patent Publication No. 8-185984 (185984/1996). The element taught in this publication includes an organic luminescent film formed of an electron transport layer, a luminescent layer and a hole transport layer, and also includes a transparent conductive layer as well as a transparent thin layer, which has a thickness of several nanometers, and is made of a metal or alloy thereof having a low work function. The thin layer is interposed between the organic luminescent film and the transparent conductive layer. Further, the transparent conductive layer (negative electrode) made of Indium Tin Oxide (ITO) is formed on the thin film, and a transparent conductive layer (positive electrode) made of ITO is disposed on the hole transport layer side thereof.
If the transparent conductive layer is used as the negative electrode, an energy gap between the negative electrode and the electron transport layer may increase excessively so that the efficiency of injection of electrons into the organic luminescent film lowers, resulting in a low luminous efficiency. For overcoming the above problem, the thin layer which has a thickness of several nanometers and is made of metal or alloy thereof having a low work function is interposed between the organic luminescent film and the transparent conductive layer.
However, manufacturing of the element of the structure disclosed in Japanese Laid-Open Patent Publication No. 8-185984 suffers from the following problem because the element employs a thin layer of metal of a low work function. It is difficult to form the thin film of the metal having a low work function. Even if such a thin film is formed, oxidization or the like is likely to occur on the thin film, and therefore it is very unstable. Accordingly, it is very difficult to form a transparent conductive layer on such a thin film of the metal having a low work function.
Meanwhile, in a camera, as an example of an optical device provided with a finder, independently provided with a shooting optical system and a finder optical system, a phenomenon which is so-called xe2x80x9cparallaxxe2x80x9d occurs as shown in FIGS. 30(A), 30(B) and 30(C). In this phenomenon, an actual shooting scope 53 of a shooting optical system 45 shifts from a finder screen 52 viewed through a finder optical system 51. According to general setting, the amount of this shift is small when a shooting distance from the camera to the shooting target is in a middle or long range, and is large when the shooting distance is short.
It is impossible to remove completely this shift in the camera which is independently provided with the shooting optical system and the finder optical system. Accordingly, as shown in FIG. 31, a parallax correction mark 54 which represents the shooting scope for the short-distance shooting is displayed on the finder screen 52 in many cases.
In the conventional camera described above, however, the parallax correction mark 54 is always displayed on the finder screen 52 shown in FIG. 31. This obstructs the view when the shooting distance is in the middle or long range and therefore the mark is not required. Such a structure has been proposed that the correction mark is displayed to show, in a dotted form, a position of a center of a shooting image when the parallax occurs. If this structure is employed together with a mechanism for macro-shooting, however, the parallax correction mark corresponding to the macro-shooting mode is displayed in the center on the finder screen, and therefore obstructs the view when viewing the shooting target during the shooting operation.
As described above, the problem relating to the parallax correction mark arises in the camera which is independently provided with the finder optical system and the shooting optical system. In addition to this problem, another problem arises, e.g., in a single-lens reflex camera in which the finder optical system is not independent of the shooting optical system. In the single-lens reflex camera, it is desired to display information relating to shooting conditions for an user on the finder screen, in addition to the foregoing shift of the shooting region on the finder screen. This additional information may be a shooting mode, a brightness of the shooting target, an autofocus region and others. The information relating to such shooting conditions is merely displayed by an LCD or by projection.
Accordingly, a back light or light source is required for information display. Further, the brightness and therefore the visibility of the shooting target image become very low when the display element is overlaid on the shooting target image.
An object of the invention is to provide an organic electro-luminescence display element having a high transparency.
Another object of the invention is to provide an organic electro-luminescence display element which entirely has a transparency, has high brightness and high luminous efficiency, and allows easy manufacturing.
Still another object of the invention is to provide an organic electro-luminescence element which has a false transparency, has high brightness and high luminous efficiency, and allows easy manufacturing.
Yet another object of the invention is to provide an organic electro-luminescence display element suitable to a finder screen display device for displaying information in a finder screen of an optical device such as a camera or another shooting device, a telescope or a microscope, which is provided with a finder (view-finder).
Further another object of the invention is to provide a finder screen display device having a good visibility.
A further object of the invention is to provide a finder screen display device, provided for a finder, which can provide a good visibility of an image viewed through the finder as well as a good visibility of information displayed by the finder screen display device.
A further object of the invention is to provide a finder screen display device which can display, with a good visibility, information relating conditions of the image viewed through a finder in an optical device, and more specifically can display the above information superimposed on the image viewed through the finder. If the optical device is, e.g., a shooting device, the above conditions relate to a shooting condition, and more specifically relate to a shift of the shooting range in the finder screen, a shooting mode, a brightness of the shooting target, an autofocus range and others.
A further object of the invention is to provide a finder screen display device achieving a good visibility of the image viewed through the finder regardless of whether the information is displayed or not.
A further object of the invention is to provide a finder screen display device, which requires neither a back light for information display nor a light source for externally illuminating displayed contents, and therefore can have a simplified structure.
A further object of the invention is to provide a finder provided with a finder screen display device, and can provide a good visibility of an image viewed through the finder as well as a good visibility of information displayed by the finder screen display device.
A further object of the invention is to provide a finder which is provided with a finder screen display device, and has a simplified structure.
A further object of the invention is to provide an optical device which is provided with a finder having a finder screen display device, and can provide a good visibility of an image viewed through the finder as well as a good visibility of information displayed by the finder screen display device.
A further object of the invention is to provide an optical device which is provided with a finder having a finder screen display device, and has a simplified structure.
The invention provides an organic electro-luminescence display element comprising:
at least a positive electrode; an organic luminescent film; an electron injection layer and a negative electrode, wherein:
each of the positive and negative electrodes is formed of a transparent conductive film;
the electron injection layer is formed of a thin film having transparency and made of
organic metal salt containing alkali metal or alkaline earth metal as the metal,
halogenide of alkali metal or alkaline earth metal, or
organic metal complex containing alkali metal or alkaline earth metal as the metal; and
the organic metal complex is at least one selected from the group consisting of acetylacetonate complex, xcex1-nitroso-xcex2-naphthol complex, salicylaldoxime complex, cupferron complex, benzoinoxime complex, bipyridine complex, phenanthroline complex, crown complex, proline complex and benzoylacetone complex.
Also, the invention provides an organic electro-luminescence display element comprising at least a positive electrode, an organic luminescent film and a negative electrode, wherein
the positive electrode is formed of an electrically conductive film having transparency, the negative electrode is formed of a metal film containing metal having a low work function, and the negative electrode is connected to a power supply lead portion made of a transparent and conductive film.
Further, the invention provides a finder screen display device, comprising:
an organic electro-luminescence element disposed in a light path near an image formation position of an image viewed through a finder, wherein
the organic electro-luminescence element is capable of displaying information in multiple colors, and
the organic electro-luminescence element is capable of displaying information superimposed on the image viewed through the finder.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.